1. Field of the Invention
The invention relates generally to clamping devices and in particular to apparatus for producing an adjustable clamping action. More specifically, the invention relates to adjustable clamps specially adapted to support fragile panels of various thicknesses, for example display panels in electronic calculators.
2. Description of the Prior Art
The novel nature of the claimed invention is evident from a comparison with the prior art. Prior art adjustable clamps having opposing jaws activated by overlying members extending to a common side of the jaws are exemplified in U.S. Pat. No. 2,862,435 and British Pat. No. 3,858, Feb. 25, 1884. The extension members of these patents, however, do not interfit, and thus lack essential aspects of the claimed invention. U.S. Pat. Nos. 2,181,831 and 3,789,724 show support and anchor devices in which interfitting members are locked together by an auxiliary element. These patents, however, do not disclose clamping apparatus in which the auxiliary element initiates adjustable clamping action.
The prior art shows no device comparable to the disclosed apparatus for the particular application of adjustably clamping and supporting variable-sized fragile display panels in electronic calculators. Moreover, the use of existing clamps for this purpose creates a number of difficulties, all of which are eliminated by the claimed invention.
Among the prior art apparatus available for clamping and supporting fragile display panels of various sizes are adjustable pliers of the standard clothespin and parallel jaws type, adjustable C clamps, and devices wherein the fragile panel is cemented to a support surface.
When used for the support of fragile panels such as glass-envelope display apparatus, these prior art clamps are unsatisfactory for a number of reasons. One problem is that the clamps are not easily adapted to maintaining a display panel parallel to a support panel such as a printed circuit board. Another problem is that the clamps apply pressure non-uniformly across the surfaces of the held panel. These non-uniform pressures create stresses which tend to crack the fragile envelope. Such non-uniform pressures result from the inherent mechanical structure of the typical prior art clamps.
In the standard plier-type adjustable clamp, the pressure-receiving ends of the dual lever system as well as the connection fulcrum are located external to the surface contours of the clamped panel. As a result, the pressure-application jaws trace out a circular arc rather than a linear path as they approach the panel surface. Because the flat jaws of such pliers are mounted at a fixed angle with respect to their associated levers, motion along a circular arc causes each jaw to contact the held panel non-uniformly at one point on the jaw rather than uniformly along the entire surface of the jaw.
Even with parallel pliers in which the jaws are configured to remain parallel to the held panel, the force-receiving ends of the dual lever system as well as the connection fulcrum are still located external to the contours of the clamped panel. This generally means that as the parallel jaws close in on the panel, the ends of the jaw surfaces closest to the fulcrum apply pressure before the remainder of the jaw surfaces do. This again is a non-uniform, fracture-inducing application of pressure.
Prior art C clamps present mounting difficulties for display panels in limited-spaced environments such as electronic calculators. Because the typical C clamp has a substantial structual protrusion beyond the contours of the member it holds, an extra volume of space in the calculator chassis is required to accommodate this protrusion. In addition, the presence of the protrusion often means that the glass envelope containing the display elements has to be mounted back away from the viewing surface. As a result, the angle of view from in front of the calculator is reduced.